The European Space Agency's Herschel and Planck space telescopes look good to go tomorrow (Thursday 14 May) at 13:12 GMT from the ESA spaceport in French Guiana.
Herschel and Planck seen in the upper stage. Pic: ESA Sitting atop an Ariane 5 ECA (see graphic), the two vehicles are ultimately destined for "L2", the second …

A-level Physics seems so long ago...

Orbits..

I think its quiet clever that you can not only orbit a mass in space (orbit around a body) but you can orbit a void point also.. Lagrange points experiancing equal/neutral gravitation... wondering how much effect the moon actually has on the earth/sun L points... I suppose that if you treat the earth+moon as one mass then it all works out fine...

@ Richard Thomas

you can oribt either a Positive or a Negative gravitational force

(Positve = a mass / Negative = a null point)

Any orbit is possible as long as it lies along a line of equal graviational pull.

The L Points have Zero Pull but as you move out from these the pull increases (away from not towards as with a mass) but as long as you are moving along an line where the pull is equal and opposite you are in orbit.

Damned cool

Go ESA!! Pity this isn't getting more press coverage. Ariane 5 is one serious launcher and Herschel and Plank constitute a major scientific experiment.

Its amazing that ESA are making some real leaps forward with technology, science etc and all we get to hear about is the bloody, creaking, crappy shuttle --- although at this time with a chance that no-one is going to get back alive ... fingers crossed for good luck.

@A-level Physics seems so long ago

L1 is easier to visualise than L2, as L2 needs to be spinning in obit, although the laws are the same.

The rotation is not round an actual physical object, but round two physical forces that interact with each other. i.e. The gravitational pulls of the Sun and the Earth.

For L1, imagine something like a tennis ball with two lengths of elastic a few meters in length tied to the opposite ends of the ball.

You then have two people, A & B, pulling on the elastic in opposite directions, putting enough tension on the elastics to lift the ball up off the ground.

Something like this: A-------*-------B

So the ball '*' represents our satellite in L1, person A is the Sun, person B is the Earth.

The ball is basically sat in the middle point of tension caused by the elastic bands. So is basically the L1 point.

Now imagine a third person walking up to the ball pulling it away from the centre and trying to throw it towards the ground. The elastic would cause the ball to start swinging around the middle point. Picture a skipping rope going round, only with a weight in the middle causing the object to continue going round and round, rather than energy being put into it by the people holding the ropes/elastics.

Obviously here on earth with friction etc. the object would slow down and the orbit/amount of swing would decrease, until finaly is was sat back in the middle stationary again. But in the vacuum of space, with no friction to slow the ball down, it just keeps swinging around and around the centre point.

So although it's not actually orbiting something physical like a planet, it is in essence orbiting the gravitations pull of both the Sun and the Earth.

L2 is the point behind the Earth, so in the example above we'd have:

A-------------B====*

So the '=' is two elastic bands, the one from the Sun 'A' and the one from the Earth 'B'.

The rules are basically the same as above for L1, but person B has to run around peson A in a big circle fast enough to cause the ball to lift off the ground due to the certifigal forces.

Again the ball would try to find the centre point and just sit there, the L2 point, but if made to orbit around this centre point like in the L1 example above, it would simple keep going round and round that point (if in the vacuum of space).